One of the problems of the electronic-type payloads on board satellites in the space environment is dissipating the heat produced by the payload.
In the case, for example, of a telecommunications satellite, the payload frequently comprises travelling-wave tubes (“TWT”), intended to amplify the signal to be transmitted with very low background noise. Now, these travelling-wave tubes release a large quantity of heat which has to be dissipated in order to avoid a rise in temperature of the payload and of the TWT itself jeopardizing its correct operation. In the case of radiative TWTs, the collector is cooled down by means of an external radiator which radiates in the infrared spectrum directly towards a colder external radiative environment. The collector of these radiative travelling wave tubes can reach a temperature of the order of 200° C. depending on its operating mode, whereas the tube itself has a temperature of a few tens of ° C.
The heat dissipation ability of a travelling-wave tube is then an element determining the power of the payload.
Before launching the satellite, ground tests are carried out on the heat dissipation of the useful payload, in a test chamber in an environment simulating the conditions encountered in space, and in particular, with simulations of a very cold or very hot environment.
During these tests, the radiative travelling wave tubes are equipped with several temperature sensors and in particular thermocouple-type temperature sensors on the radiator. These sensors are fixed onto a metal plate with glue.
However, these sensors measure the surface temperature of the radiator with significant errors, typically 45° C. when the collectors of the travelling-wave tubes have a temperature of 150° C. in a test chamber at −50° C.: these errors result from the fact that the thermocouple measures its own temperature and that the temperature of the junction (or weld) of the thermocouple reaches equilibrium between the temperature of the substrate measured and the external radiative environment. The conductive leak in the thermocouple wires is the main contributor to the measuring error.